In the field of graphic arts, a system of forming an image with high contrast photographic characteristics is required so as to improve the reproduction of an image with continuous gradation by dot images or the faithful reproduction of a line image.
Hithereto, a particular developer which is called a lith developer has been used for the purpose. The ligh developer contains only hydroquinone as a developing agent and contains only hydroquinone as a developing agent and contains a preservative in the form of a sulfite/formaldehyde adduct so that the concentration of the free sulfite ion in the developer is made extremely low so as not to interfere with the infectious developability of the developer. Accordingly, the lith developer has a serious defect that it is extremely easily oxidized with air and cannot be preserved for a long period of time, i.e., more than 3 days.
Under the circumstances, noticeable efforts have been made so as to obtain effective means of stably maintaining the activity of the developer. Various alternative photographic systems capable of overcoming said problems and forming images with high contrast photographic characteristics have been proposed.
As a means of forming an image with high contrast photographic characteristics by the use of a stable developer, for example, there are the methods of using a hydrazine derivative as described in U.S. Pat. Nos. 4,224,401, 4,168,977, 4,166,742, 4,311,781, 4,272,606, 4,211,857 and 4,243,739.
In accordance with said methods, a silver halide photographic material containing a particular hydrazine derivative is processed with a developer containing a sulfite preservative in an amount of 0.15 mol/liter or more, at pH 10.5 to 12.3, and the photographic material has a high sensitivity and may form an image with high contrast photographic characteristics. Further, as the developer may contain a sulfite of a high concentration, the stability of the developer against aerial oxidation is far higher than that of a ligh developer. In addition, the development time may noticeably be reduced.
In general, an automatic developing machine is used for processing the high contrast silver halide photographic materials of this kind. As automatic developing devices for black-and-white silver halide photographic materials, heretofore a suspended automatic developing machine, a processing machine for motion picture film, a roller-conveying automatic developig machine, a rotary automatic developing machine for disc film, a rotary drum automatic developing machine and a reel-combined automatic developing machine have been put to practical use. These automatic developing machines are equipped with tanks for housing a developer, a fixer, a stabilizer, a bleaching solution and optionally a stopping solution, an adjusting solution and a reversing solution. Ideally, it is desired to protect these solutions, except the bleaching solution, from oxidizing and aging due to contact with air. However, as the respective surface area of the respective processing solutions to be contacted with air is large. Accordingly, there is a problem of noticeable deterioration and evaporation of processing solutions because of aerial oxidation. In particular, in the field of photomechanical processes where typical black-and-white silver halide photographic material sheets are mostly used, a roller-conveying type automatic developing machine having a large open area ratio (K) is mainly used because of the easy operatability, rapid processability and simple processability. The open area ratio (K) cm.sup.-1 as referred to herein means a value of the air contact surface of processing solution (S) cm.sup.2 as divided by the volume of the solution (V) cm.sup.3 and is represented by the following equation: EQU K=S/V(cm.sup.-1)
The structure of the roller-conveying type automatic developing machine is as shown in FIG. 1, where the taking-in conveyors rollers and/or the taking-out conveyor rollers are kept in contact with both the developer and air. More precisely, FIG. 1 (a) shows one embodiment where all the nip rollers (5) and (6) in the taking-out side and the nip rollers (3) and (4) in the introduction side are partly dipped in the processing solution; and FIG. 1 (b) and FIG. 1 (c) shows other embodiments where the nip roller (6) in the exciting side is partly dipped in the processing solution. Such structure is required so as to accelerate the conveyance time and to prevent the dot image from being disordered and the line image from being cut.
In the roller-conveying type automatic developing machine of said system, the open area ratio (K) is required to be investigated in two cases. Precisely, the open area ratio (K.sub.S) while the rollers are not moved (or static) is represented by the following equiation (1) in consideration of only the horizontal liquid area (S.sub.1) which is directly contacted with air. EQU K.sub.s =S.sub.1 /V (1)
On the other hand, the open area ratio (K.sub.D) while the rollers are being moved (or dynamic) is represented by the following equation (2). since the surface area of the liquid (S.sub.2) which is on the surface of the rollers above the liquid surface is to be taken into consideration together with the horizontal liquid area (S.sub.1). EQU K.sub.D =(S.sub.1 +S.sub.2)/V (2)
In the roller-conveying type automatic developing machines which have heretofore been put to practical use, K.sub.S is from 0.03 to 0.15, K.sub.D is from 0.05 to 0.20, and K.sub.D /K.sub.S is from 1.2 to 5. In general, the rollers are not rotated when no development is carried out, so that the liquid on the surface of the rollers evaporates, and the residues form deposits on the rollers.
An ultra-hard processing system in which a silver halide photographic material containing at least one hydrazine derivative is processed with a dihydroxybenzene developer containing a sulfite preservative in an amount of 0.15 mol/liter or more at pH 10.5 to 12.3 is a system having greatly more improved stability and rapid processability than a conventional lith development system. However, when the system is carried out by the use of a roller-conveying type automatic developing machine with a high open area ratio, there are still various problems as mentioned below.
(a) As the processing solution has a high pH value, the solution is easily oxidized with air in a roller-conveying type automatic developing machine with a high open area ratio so that the developing agent and the preservative used are rapidly deteriorated.
(b) The processing solution easily absorbs carbon dioxide from the air and thus the development activity of the solution often varies in accordance with the variation of the CO.sub.2 concentration in the surrounding atmosphere. In particular, under winter like circumstances where gas, petroleum and stoves are much used, the pH value of the developer would drop so that the variation of the photographic characteristics would become noticeable in some photographic materials.
(c) Water is readily evaporated and the solution is easily concentrated. The photographic characteristics of the processed photographic materials would vary because of the variation of the concentration of the processing solution.
(d) In order to compensate for the variation of the concentration of the processing solution, a large amount of replenisher is required.
Because of evaporation of solvent and concentration of chemicals in the processing solution, the liquid level is lowered, the solids content dries and forms deposits which would adhere to rollers and gears and would cause stains or development blurs as well as mechanical accidents in the developing machine.
In order to overcome said problems, provisions of a floating lid ((7) in FIG. 1 (b) or 1 (c)) to cover the complete surface of the processing solution has been proposed, with the floating lid being removed during development, or provision of floating lids on the surface parts of the processing solution except at the surface where the photographic material passes through and where the photographic material-conveying device part in the tank communicates with the surface has also been proposed. In the former case, however, it is extremely troublesome and complicated to arrange and remove the floating lid in the automatic developing machine. In the latter case, the area of the surface of the processing solution to be covered by the floating lids is small, since the solution tank is equipped with rollers, and therefore, the effect of preventing aerial oxidation by the floating lids would be substantially small. For these reasons, neither of the two approaches could be said to satisfactorily overcome the problems. In addition, when the floating lids were arranged on the surface of the processing solution, these would rotate on the liquid surface during running of the developing machine, and therefore, a bad influence of substantially increasing the surface area of the processing solution is inevitable because of the provision of the lids.
On the other hand, there is another method in which the surface of the developer in an automatic developing machine is covered except at the inlet and outlet parts for the photographic material to be processed so that the area of the solution to be contacted with water may be reduced. However, the method is often accompanied by problems on the operability of the developing machine.